These units charge on 12V DC external power (+ tip polarity). The voltmeter shows a precise 12 volts from my AC adapter when plugged in, but a car alternator typically provides 13-14V to the battery when the engine is running.

That being said, you might get by with a direct "Pass-through" type of adapter, but the hardest thing would be to find the right sized power connector on the end. You should check the exact voltage at the tip with the car running before connecting just to be sure. If a pass-through provides adequate polarity/voltage, then there would be no problem with the current (amps), as there would be plenty.

If instead you find a 12 V output auto adapter, be sure that it delivers at the very least 2 amps, but preferably 3+ amps. The package and/or the unit itself should have output max amperage listed (If listed in milliamps then multiply by 1000 for amps)

Both of the above approaches MIGHT work. There is an easy way to run in a car that WILL work. You can get a fairly inexpensive power inverter that converts your 12-15v DC from the lighter plug to a nice solid 120VAC. Then you can just plug the standard AC adapter into that. This results in a few more wires to manage, but it provides reliable power.DAM